Adding and removing your address is fine and the welcome mails go out correctly while redirecting you to a separate welcome page. Removing your address provides a prompt rather than redirecting to a separate page.
Each address in the list is added as a BCC to preserve subscribers privacy. Using
wp_mail they are each added as a separate header item so I have to loop through them individually. As an additional privacy measure I might look at encrypting the addresses in the database but that's for another day.
It's a bit rough and ready, and could probably be made a little (okay, a lot) prettier, but it seems to do the trick.